The broad long-term objective of this competing renewal application is to develop novel prodrug strategies to improve ocular antiviral drug therapy via membrane transporters/receptors. In the previous grant period, a series of acyl and amino acid derivatives of acyclovir (ACV) were evaluated for efficacy against herpes simplex virus type I (HSV-1), and cytomegalovirus infections. Although the lipophilic acyl ACV prodrugs are highly permeable across the lipoidal corneal epithelium, poor aqueous solubility and limited stability renders these compounds unsuitable for topical instillation. Therefore therapeutic concentrations of ACV cannot be achieved from a solution dosage form of these prodrugs limiting the antiviral efficacies in corneal epithelium and stroma. A novel approach utilizing peptide (PEPT1/PEPT2), amino acid and monocarboxylic acid transporter (MCT) for ocular delivery of ACV has been developed. We have identified for the first time these transporters on the intact rabbit cornea as well as corneal epithelial cell line (SIRC). Dipeptide prodrugs (Gly-Gly and Val-Val) of ACV (US patent pending) have shown excellent in vitro antiviral activity against HSV 1 in HFF cells and in vivo rabbit epithelial keratitis with no measurable cytotoxicity. This discovery constitutes significant therapeutic advantage over the current therapy using highly cytotoxic trifluorothymidine (TFT). The dipeptides (Gly-Gly, Val-Val, Val-Gly, Gly-Val) of ACV exhibit high aqueous solubility and good stability at pH 5.6 (Val- Val ACV and Gly-Gly ACV showing no measurable degradation in 7 days allowing stable aqueous formulations in pH 5.0-6.0 up to 30 mg/ml concentration. Application of such high concentrations of dipeptide or glutamate esters of ACV may also eradicate stromal infection, which is not adequately treated by current antiviral therapeutic regimens. The proposed prodrugs are much more stable and may be more permeable compared to valacyclovir. Recently, our laboratory has identified folate receptors on the rabbit corneal epithelial cell line. We propose to synthesize a series of dipeptide, amino acid, monocarboxylate and folate esters to take advantage of the PEPT1/PEPT2, amino acid, MCT and folate receptor/transporter respectively on the corneal epithelium to deliver a model antiviral agent, ACV which has poor ocular bioavailability. The specific aims of the proposal are: 1. to synthesize derivatives of ACV targeting peptide, amino acid, MCT and folate transport systems and characterize the physiochemical properties i.e., aqueous solubility, octanol/water partition coefficient, stability, and biochemical pharmacology (bioreversion and metabolism) of these compounds in ocular fluids and cell homogenates including cornea, iris-ciliary body, lens, aqueous humor, vitreous humor and retina/choroid, 2. to study uptake, transport and simultaneous metabolism of the dipeptide, amino acid, folate, and carboxylate ester prodrugs of ACV across isolated rabbit cornea and rabbit corneal epithelial cell line (SIRC), 3. to evaluate in vivo ocular bioavailability of the compounds in the anterior chamber utilizing ocular microdialysis technique in anaesthetized and conscious rabbit models following topical administration, and finally, 4. to evaluate antiviral efficacy and cytotoxicity of the proposed compounds against in vitro viral screens of HSV-1, HSV-2, CMV, VZV, and EBV by NIAID supported contract at University of Alabama, Birmingham (P.I. Dr. Earl Kern). In vivo antiviral efficacies will be evaluated in rabbit HSV-1 McKree strain acute epithelial and stromal keratitis model by Dr. James Hill at the LSU Eye Center, New Orleans, LA